It's great!
It's alot different than AC2 and it's two expansions. The story progression slows down quite a bit in comparrison, and that's a good thing.
Where in AC2 you have this long list of targets to go put down one by one in a bunch of different missions, AC3 gives you only a handful; and the leadup to each assassination is more worthwhile, since you feel more like you are accomplishing something because of how hard you worked to get it. The game builds up little by little until about in the middle of the story everything explodes on you and the world is all expanded and most of your side quests are available.
The side quests in themselves are more fun than in AC2. AC2 (the expansions Brotherhood and Revelations tried to improve on this, I think Brotherhood did it the best out of the three with the Roman guilds side stories) just gives you a bunch of missions on the minimap you can go do at your leisure. AC3 has a few of these, but most of them revolve around either recruiting assassins, or people to live on your property so you can trade their goods for new stuff, which is the only way to get the best weapons. There's also more interesting side questing mechanics such as the frontier area in general, and naval battles. This way you can grind money all you want, you won't get all the best gear without doing other crap, so if you skip the side story you can still beat the game, it will just be harder.
Also I like Connor as a character better than Ezio. Ezio was born a punk-ass kid with a good life, and his whole story is about returning to that good life which was taken from him, he just ended up changing (somewhat) along the way. Ezio is fun to watch, because he's just a badass; but that's all he is, and there's nothing that can be done to change it. Connor is a much different story, with more tragedy a deeper story overall, and I enjoyed watching it more.
Also the online mode is much better than Brotherhood and Revelations.
